The present invention relates to a linear actuator and, more specifically, to a linear actuator which incorporates flat magnets.
A typical linear actuator of the prior art consists of a housing which encloses a cylindrical coil and a cylindrical magnet. The coil and magnet are disposed about a shaft or armature which moves axially within the housing. When the coil is not energized, the shaft is in a first position. When the coil is energized, the shaft moves axially to a second position. The sealing force, the force maintaining the shaft in either the first or second position, is created by a magnet which passes magnetic flux through the shaft. The strength of the sealing force is a function of the amount of air gap between the shaft and the magnet. Sealing force decreases as the air gap between the magnet and the shaft increases. Magnetic flux is also transferred through elements of the housing. Accordingly, the sealing force also decreases as the total air gap between the magnet and the housing components increases.
Because the amount of force exerted on the shaft is a function of the air gap between the magnets and the shaft and/or the total air gap between the magnet and the components of the housing, it is desirable to minimize the air gap. As shown in FIG. 1, prior art linear actuators use cylindrical magnets 1 having a cylindrical hole therethrough. The cylindrical magnet is typically held on a magnet carrier 2 which is disposed within the cylindrical hole, between the magnet and the shaft 3. The magnet is further enclosed within a protective housing 4. Thus, there are three circular interfaces in linear actuators in the prior art. It is difficult, however, to machine components having tight tolerances with a cylindrical interface. As shown on FIG. 1, circular holes may be slightly elliptical or oversized, resulting in an air gap 5,6, 7. The sealing force created by the magnet could be increased if the air gap 5, 6, 7 between the shaft and magnet and/or the total air gap between the magnet and housing could be reduced. Additionally, production costs could be reduced if the cylindrical interface were not used.
Therefore, there is a need for a linear actuator that reduces the air gap between the magnet carrier and the shaft.
There is a further need for a linear actuator that reduces the total air gap between the magnet and the housing components.
There is a further need for a linear actuator that is easily manufactured with a minimal air gap.
These needs and others are satisfied by the present invention, which is directed to a linear actuator, which utilizes a plurality of flat magnets spaced about the linear actuator""s shaft
As with prior art linear actuators, the invention includes a housing which encloses a coil and which has a shaft passing through the coil and housing. In place of the typical cylindrical magnet, however, is a plurality of flat magnets. The flat magnets are sandwiched between a magnet support ring, which forms a portion of the housing, and a magnet carrier which is adjacent to the shaft. Because the magnets are flat, both the magnet support ring and the magnet carrier are easily machined so that the average gap between the magnet and either the magnet support ring or the magnet carrier is less than 0.001 inch. Additionally, because the magnets are flat, the present invention, requires only one circular interface, unlike the prior art which includes three circular interfaces. With a smaller air gap between the flat magnets and their support structures, the actuator provides a greater sealing force.